This invention relates to vehicular power methods and systems and more particularly, it concerns hybrid vehicle power methods and systems in which a combination of generated and stored power is used for vehicle propulsion.
Hybrid vehicle power systems which combine a primary power source or engine with an energy storage device, such as a flywheel, are prevalently disclosed in prior publications and issued patents. Although the use of such hybrid power systems in the past has been limited and primarily experimental, recent emphasis on fuel economy and reduced air pollution by automotive engines has justified a renewed interest in this approach to vehicular propulsion. It is well known, for example, that fuel economy can be maximized by achieving maximum operating efficiency of automotive internal combustion engines. While technology exists for optimizing the efficiency of an internal combustion engine, it is difficult if not impossible to increase engine efficiency without also increasing the percentage of air pollutants, particularly nitrogen oxides, discharged with the exhaust gases of the engine. Hybrid power systems offer a potential answer to this dilemma by permitting an engine to be operated at increased efficiency during periods of time when power generated by engine operation is needed and also to store sufficient energy in a flywheel so that the vehicle may be driven during limited periods of times with the engine shut off. In other words, such hybrid power systems provide an answer to fuel economy by increasing engine efficiency and also an answer to reduced air pollution by reducing the duration of engine operation for a given time of vehicle operation.
It is known, for example, that a simple flywheel represented by a carbon steel disk 3 cm. in thickness and between 40 and 46 cm. in diameter, when rotated at speeds of between 6,000 RPM and 8,000 RPM will provide sufficient energy to propel a conventional automotive vehicle for short distances or start an automotive engine after it has been shut off for moderate durations of time such as the time intervals incurred under city driving conditions when a vehicle is stopped due to traffic conditions. These factors, combined with the facility for storing the kinetic energy of vehicle momentum by driving the flywheel during at least initial stages of vehicle braking, make it clear that the energy storing capabilities of such a flywheel could result in substantial fuel savings and reduction of air pollution by automotive engines simply by reducing the total time of engine operation and limiting periods of engine operation where engine efficiency is low.
It is also known, however, that the transfer of kinetic energy to or from the flywheel of a hybrid system requires an infinitely variable or I.V. transmission in order that the rotational speeds of the flywheel may be related to the rotational speeds at which power must be transmitted to or be absorbed from an automotive driveshaft, for example, smoothly and without loss of energy. Heretofore, the I.V. transmission has represented not only a weak link in the power train of hybrid power systems, but also, an additional component in the power train and a source of potential mechanical problems separate from those associated with the flywheel.
The state-of-the-art relating to I.V. transmissions has been developed to a stage where energy transfer to and from a flywheel rotating at moderate speeds can be accomplished efficiently and effectively within the operating parameters of a hybrid vehicular power system. In a commonly owned, co-pending U.S. application Ser. No. 706,291, filed July 19, 1976 by Yves Jean Kemper now U.S. Pat. No. 4,152,946, for example, several embodiments of an I.V. transmission are disclosed in which the inertial forces of moving bodies or components are resolved in a manner to augment the normal force by which rolling traction surfaces on two of three relatively movable bodies may transmit torque with an infinitely variable ratio of output/input speeds. The I.V. transmissions disclosed in this co-pending application, moreover, permit a wide range of speed ratios and are capable of power transmission at high efficiencies.